Re: [Xen-devel] [PATCH v2] tools/xenconsoled: Increase file descriptor limit

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Tue, Feb 17, 2015 at 04:21:24PM +0000, Andrew Cooper wrote:
> XenServer's VM density testing uncovered a regression when moving from
> sysvinit to systemd where the file descriptor limit dropped from 4096 to
> 1024. (XenServer had previously inserted a ulimit statement into its
> initscripts.)
> 
> One solution is to use LimitNOFILE=4096 in xenconsoled.service to match the
> lost ulimit, but that is only a stopgap solution.
> 
> As Xenconsoled genuinely needs a large number of file descriptors if a large
> number of domains are running, and is well behaved with its descriptors,
> attempt to up the limit to the system maximum.
> 
> Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
> CC: Ian Campbell <Ian.Campbell@xxxxxxxxxx>
> CC: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>
> CC: Wei Liu <wei.liu2@xxxxxxxxxx>
> 
> ---
> v2:
>  * Always increase soft limit to hard limit
>  * Correct commment regarding number of file descriptors
>  * long -> unsigned long as that appears to be the underlying type of an 
> rlim_t
> ---
>  tools/console/daemon/main.c |   45 
> +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 45 insertions(+)
> 
> diff --git a/tools/console/daemon/main.c b/tools/console/daemon/main.c
> index 92d2fc4..0bb9d8a 100644
> --- a/tools/console/daemon/main.c
> +++ b/tools/console/daemon/main.c
> @@ -26,6 +26,7 @@
>  #include <string.h>
>  #include <signal.h>
>  #include <sys/types.h>
> +#include <sys/resource.h>
>  
>  #include "xenctrl.h"
>  
> @@ -55,6 +56,48 @@ static void version(char *name)
>       printf("Xen Console Daemon 3.0\n");
>  }
>  
> +/*
> + * Xenconsoled requires two file descriptors for each PV console (pty and log
> + * file), which can easily exceed the default of 1024 if many guests are
> + * running.  Try to set the fd limit to the system maximum, falling back to a
> + * default of 4096.
> + */
> +static void increase_fd_limit(void)
> +{
> +     FILE *fs_nr_open;
> +     struct rlimit lim;
> +     unsigned long nr_open = 4096;
> +
> +     if (getrlimit(RLIMIT_NOFILE, &lim) < 0)
> +             return;
> +
> +     /* Increase the soft limit to the current hard limit. */
> +     if (lim.rlim_cur < lim.rlim_max) {
> +             lim.rlim_cur = lim.rlim_max;
> +             if (setrlimit(RLIMIT_NOFILE, &lim) < 0)
> +                     return;
> +     }
> +
> +     /* Attempt to locate the system maximum. */
> +     fs_nr_open = fopen("/proc/sys/fs/nr_open", "r");
> +     if (fs_nr_open) {
> +             unsigned long nr;
> +
> +             if (fscanf(fs_nr_open, "%lu", &nr) == 1)
> +                     nr_open = nr;
> +             fclose(fs_nr_open);
> +     }
> +
> +     /*
> +      * In the likely case that we are a root process with
> +      * CAP_SYS_RESOURCE, attempt to up our hard limit.
> +      */
> +     if (nr_open > lim.rlim_max) {
> +             lim.rlim_cur = lim.rlim_max = nr_open;
> +             setrlimit(RLIMIT_NOFILE, &lim);
> +     }
> +}
> +

This function looks Linux centric (/proc and CAP_SYSRESOURCE). Please be
considerate to other Unices. :-)

Also you might want to log failures along the line.

Wei.

>  int main(int argc, char **argv)
>  {
>       const char *sopts = "hVvit:o:";
> @@ -154,6 +197,8 @@ int main(int argc, char **argv)
>       openlog("xenconsoled", syslog_option, LOG_DAEMON);
>       setlogmask(syslog_mask);
>  
> +     increase_fd_limit();
> +
>       if (!is_interactive) {
>               daemonize(pidfile ? pidfile : "/var/run/xenconsoled.pid");
>       }
> -- 
> 1.7.10.4

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